1. Field of the Invention
The present invention relates to mobile radio receiving installations. More particularly, it relates to a circuit for testing the operating functions of mobile radio receiving installation having at least one receiving antenna that is connected to a superheterodyne receiver equipped with an image frequency filter, and a measuring device for detecting the receiving signal level.
2. The Prior Art
In a practical application of radio receiving installations, there is a frequent problem of partial losses due to the aging of components and connectors. Unfortunately, these losses are difficult to detect during operation. Specifically, in a superheterodyne receiver, the feed line between the antenna and the receiver, and/or the antenna installation suffer from this aging problem.
When working with complicated receivers having a plurality of antennas and a diversity of systems, the testing of individual components is extremely costly due to their limited accessibility. According to the state of the art, test signals are used in the testing mode where the components of the installation, or the series circuit of the components, can be tested for proper functioning.